1. Field of the Invention
The present invention relates generally to data communication by way of power lines and more particularly to a system for transmitting and receiving high frequency data signals over a low frequency (60 Hz) utility power line.
2. Prior Art
Power line communication systems have been in use for quite some time providing telephone service in remote rural areas or for remote control of appliances, lights, security alarms, garage door openers, electrical outlets, etc. Power line communication systems are affected in general by three major factors, namely, noise, isolation and complexity. Noise is perhaps the biggest problem as utility power lines carry a great deal of electrical noise which affects the system readability of the high frequency carrier signal superimposed on the low frequency (60 Hz) alternating current (AC) power line. To overcome this problem multiple transmissions of the same block of data are usually required to assure that the receiving device responds correctly to the transmitted data. Furthermore, once a transmission signal is placed on the power line, it appears everywhere on the power line distribution system. To prevent this from happening, isolation devices maybe inserted in series with the power distribution system to carry the full current thereof. Such isolation devices are usually costly to purchase and maintain in the long run. In some cases, a great deal of cross-talk is present between various units or buildings connected on the same power line distribution system. To overcome these problems, power line transmitters and/or receivers usually include complex circuitry which raises manufacturing costs and is usually limited to a few specific applications, i.e. it is not readily adaptable to a wide variety of operational conditions.
Power line communication also offers certain advantages to the power user. For example, by utilizing existing power lines as means for data communication between transmitters and receivers within a building, such systems may be installed on site without the need for additional wiring. Moreover, utilizing power lines for communication also provides a greater physical range of control than may be available via known infrared, ultrasonic or RF control systems.
The conventional power line communication scheme involves a receiver connected between the power line and each device to be controlled thereof and a plurality of transmitters connected to the power line for transmitting data signals to the receivers. Data is transmitted in a synchronized fashion at a modulation frequency generally much greater than the 60 Hz AC power line frequency, e.g., 120 kHz, with each transmission word usually including a start code, an appliance or house code and an operation code whereby each code is composed of a predetermined number of data bits. Various power line data communication protocols are in use today, however, none is capable in conjunction with its associated hardware of providing an inexpensive and effective power line communication solution to the average user which may be implemented in a wide variety of operational conditions.
Therefore, the need arises for an improved power line communication system which does not use isolation devices, is capable of transmitting and receiving high frequency data signals from the power line accurately and efficiently and is easily adaptable to a wide variety of operational conditions. Such a communication system should preferably use an improved data communication protocol which can effectively handle data transmissions in any kind of environment.
The present invention meets the above needs and is directed to a power line communication system, comprising a processor for encoding digital data into phase packets; a sine wave approximator operatively coupled to the processor for generating a high frequency sine wave-shaped communication signal on command by the processor; means for superimposing the generated high frequency sine wave-shaped communication signal on a low frequency alternating current (AC) power line; means for decoupling the superimposed high frequency sine wave-shaped communication signal from the low frequency AC power line; means for filtering the decoupled high frequency sine wave-shaped communication signal; means for digitizing the filtered decoupled high frequency sine wave-shaped communication signal; and a demodulator operatively coupled to the processor for receiving and demodulating the digitized high frequency communication signal, the demodulated high frequency communication signal sent to the processor for communication data recognition.
In accordance with one aspect of the present invention, the processor includes means for error detection of the sent demodulated high frequency communication signal.
In accordance with another aspect of the present invention, the superimposing means includes a transconductance amplifier operatively coupled to the sine wave approximator for receiving and superimposing the generated high frequency sine wave-shaped communication signal on the low frequency AC power line and drawing current through a bridge rectifier, the bridge rectifier operatively coupled to the low frequency AC power line.
In accordance with yet another aspect of the present invention, the decoupling means includes a high-pass filter operatively coupled to the bridge rectifier for receiving and decoupling the superimposed high frequency sine wave-shaped communication signal from the low frequency AC power line.
In accordance with still another aspect of the present invention, the filtering means includes a first band-pass filter operatively coupled to the high-pass filter for receiving and filtering the decoupled high frequency sine wave-shaped communication signal. The filtering means further includes a second band-pass filter operatively coupled to the first band-pass filter for receiving and filtering the filtered high frequency sine wave-shaped communication signal from the first band-pass filter.
In accordance with a further aspect of the present invention, the digitizing means includes a digitizing comparator operatively coupled to the second band-pass filter for digitizing the filtered decoupled high frequency sine wave-shaped communication signal, the digitized signal being a 1-bit in phase signal or a 1-bit 90xc2x0 out of phase signal.
In accordance with a still further aspect of the present invention, the demodulator comprises a D-flip flop and a quadrature generator for receiving the 1-bit in phase and the 1-bit 90xc2x0 out of phase signals from the digitizing comparator, the quadrature generator generating a first in phase output signal and a second 90xc2x0 out of phase output signal. The demodulator further comprises first and second digital integrators for detecting the first in phase output signal and the second 90xc2x0 out of phase output signal.
In accordance with a different aspect of the present invention, the power line communication system comprises a frame generator operatively coupled to the first and second digital integrators for generating a series of cell frame interrupt signals for the processor.
In accordance with a still different aspect of the present invention, the power line communication system further comprises a data compressor operatively coupled to the first and second digital integrators for compressing received data signals.
In accordance with an alternative aspect of the present invention, the power line communication system further comprises an application-specific integrated circuit (ASIC) coupled to the processor by way of a data bus. The ASIC includes a field-programmable gate array (FPGA), the FPGA including the demodulator and the sine wave approximator.
The present invention is also directed to a power line communication method, comprising the steps of:
(a) generating a sequence of fixed length and fixed frequency data cells, each data cell of one of four phases 0xc2x0, 90xc2x0, 180xc2x0 or 270xc2x0 relative to the phase of a preceding transmitted cell, the first cell in the sequence designated zero-phase reference cell;
(b) transmitting the sequence of fixed length and fixed frequency data cells over the AC power line, the transmitted cells synchronized by zero voltage crossings on the AC power line and distributed over the half cycle of the AC power line, the zero-phase reference cell carrying no data;
(c) receiving the transmitted data cells off the AC power line, each transmitted data cell evaluated for phase shift relative to a preceding transmitted data cell;
(d) detecting the signal phase of the received data cells;
(e) extracting the phase angle from the detected data cells;
(f) recovering the data from the extracted phase angle information; and
(g) checking the recovered data for data integrity errors.
These and other aspects of the present invention will become apparent from a review of the accompanying drawings and the following detailed description of the preferred embodiments of the present invention.